The invention described herein was made by an employee of the United States Government, and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
The invention relates generally to bearings, and more particularly to a one-way bearing that permits relative rotation of two machine components or the like in one direction while preventing rotation in the opposite direction.
2. Background Art
One-way bearings are commonly used in drive trains for vehicles, such as automobile and truck transmissions. One-way bearings may also be used in materials handling devices, such as elevators, cranes, and fork lifts. They may be employed in spacecraft, e.g., in rotating solar array panels, and aeronautics, e.g., in helicopters or tilt-rotor aircraft.
Typically, one way bearings include a first pair of dedicated concentric races containing sprags and a second pair of dedicated concentric races containing rolling bearings. The use of two different dedicated sets of races for the sprags and the rolling bearings adds to the size of typical one-way bearings, and may render them undesirable for certain applications.
Sprags typically used in one-way bearings may lack the strength for certain applications, reducing the effectiveness of the one-way bearing in preventing rotation in the non-preferential direction. Furthermore, typical sprags may not be suitable for use with certain lubricants. For example, in applications in outer space it may be necessary to use a lubricant to reduce friction between the sprags and races. The lubricant may hinder the ability of the typical sprags to prevent rotation of the bearing in the non-preferential direction.
Pawls have been used instead of sprags, but addition of pawls between a pair of dedicated concentric races significantly increases the size of a bearing. Pawls may have increased strength to prevent rotation of the one-way bearing in the non-preferential direction of rotation, as compared to typical sprags. However, pawls may not engage between the pair of races as quickly as typical sprags, and thus may not prevent rotation of the one-way bearing in the non-preferential direction as quickly as sprags. Delay in preventing rotation in the non-preferential direction may cause the pawls to impact and possibly damage or cause wear to the races.
The rolling bearings used in one-way clutches often are ball bearings. However, ball bearings may not be strong enough for certain applications, in particular applications where high thrust or axial loads are required to be transmitted by the bearings. Crossed roller bearings have been used for applications having axial loads, but can be expensive and may not be suitable for high speed applications. The strength advantages of crossed roller bearings may also be limited when tilt and radial loads must be transmitted in addition to axial loads.
Accordingly, there remains a need for a compact, high strength one-way bearing suitable for applications requiring rapid prevention of rotation in the non-preferential direction, while also able to withstand tilt, radial, and axial loads.
In accordance with the invention, an apparatus and method are provided for allowing relative rotation between an inner member and an outer member in a preferential direction and preventing rotation in an opposite, non-preferential direction. The apparatus and method are preferably embodied in a one-way bearing configured to minimize its size, provide sufficient locking force when rotated in the non-preferential direction, and withstand axial, radial, and tilt forces.
The one-way bearing comprises a single, dedicated pair of concentric races. Positioned between the races are both anti-rotation members and rolling bearing members. Providing only a single pair of dedicated concentric races for both the anti-rotation members and the rolling bearing members eliminates the need for two separate pairs of dedicated concentric races, thus enabling a more compact one-way bearing design.
The single pair of dedicated races include an inner race and an outer race. Each of the inner and outer races may include two separate sets of engagement surfaces. The anti-rotation members may be positioned to engage a first set of engagement surfaces, and the rolling bearing members a second set of engagement surfaces. Providing separate engagement surfaces for the anti-rotation members and the rolling bearings may reduce wear, provide smooth operation, and increase bearing life.
The engagement surfaces may comprise a pair of concentric grooves. A first concentric groove may be configured for engagement with the anti-rotation members and a second concentric groove may be configured for engagement with the rolling bearing members. The first groove may extend to a first depth. The second groove may begin at the first depth and extend to a second depth.
In an aspect of the invention, a carrier is positioned between the dedicated pair of concentric races. The carrier may function to maintain the anti-rotation members operationally separate from the roller bearing members. The carrier may ensure that the operation of the anti-rotation members does not interfere with the operation of the roller bearing members. Dividers may be integrally formed with the carrier to maintain the anti-rotation members operationally separate from the roller bearing members.
The anti-rotation members may comprise sprags. The sprags may be three-dimensional sprags, although conventional sprags or two-dimensional sprags may also be used. The sprags may have a first or free-wheeling orientation, permitting rotation in the preferential direction. In the first orientation the sprags may contact the engagement surfaces of the second groove in a free-wheeling arrangement, permitting the inner and outer races to rotate relative to each other. The sprags may also have a second or locking orientation, preventing rotation in the non-preferential direction, wherein the sprags contact the engagement surfaces of the groove in a locking manner.
The carrier may include spring members for maintaining the sprags in their first orientation during rotation in the preferential direction. The spring members may be selected to impart spring forces to the sprags effective to allow for relative rotation between the inner and outer races in the preferential direction with minimal or no resistance. However, the spring forces may preferably be selected to allow the sprags to readily move from their first orientation to their second orientation, whereby the sprags prevent relative rotation between the inner and outer races in the non-preferential direction.
The spring members may be integrally formed with the carrier. Integrally forming the carrier and spring members can increase simplicity in manufacturing and assembling the apparatus of the invention. In a preferred aspect of the invention, the carrier and integral spring members may have a one-piece construction, further simplifying manufacturing and assembly of the apparatus. The one-piece carrier with integral spring members may be formed from a plastic or polymer, and may be formed using extrusion techniques.
The spring members may be separate from the carrier. The spring members may be provided between the sprags and surfaces of the carrier to bias the springs into the first orientation. The sprags may include a recessed groove or slot for at least partially securing the spring member therein.
In yet another aspect of the invention, a single spring member may be used to bias all of the sprags into the first orientation. A pair of fingers extending from a side of the sprags may be configured to receive the spring member therebetween to bias the sprags into the first orientation. In addition, the spring member may maintain the sprags and rolling bearings operationally separate, thereby eliminating the need for a separate carrier member.
According to an aspect of the invention, the rolling bearings may comprise thrust rollers. The thrust rollers may be positioned between the inner and outer races. Thrust lips may be formed on both the inner and outer races to maintain the thrust rollers in position between the races. The thrust lips and thrust rollers may combine to transmit axial, tilt, and radial loads between the inner and outer races.